In order to cover identical zones on the surface of the globe using two radiated waves at different frequencies, a known antenna is constituted by a reflector of paraboloid shape situated opposite a primary source of electromagnetic waves placed at the focus of the reflector, the primary source being horn-shaped, for example, and being placed at the end of an electromagnetic waveguide.
Since the radiation pattern of the primary source has an aperture which varies as a function of the frequency of the radiated electromagnetic wave, this type of implementation provides an antenna whose efficiency is not the same for both of the waves reflected by the reflector, and in order to obtain signals of the same energy at the surface of the globe, the primary source must be adapted to compensate for the energy loss to which one of the waves is subjected relative to the other, with such compensation requiring the transmitter power supply devices in the satellite to be over-dimensioned.
Further, known antennas comprising a single reflector do not conserve completely orthogonal electric fields in each of their planes of polarization after reflection, so the isolation between the transmission channels constituted by the waves of different frequency cannot be totally effective.
Preferred embodiments of the present invention remedy these drawbacks.